There's nothing like the sting of regret felt as we stumble out of a stranger's apartment to the harsh glare of the morning, dressed in the clothes we were wearing 24 hours earlier. But it seems the fairer sex feels that sting quite a bit more, and, supposedly, that side dish of regret accompanying so many sexual liaisons is a product of thousands of years of evolution.

Research done by psychologists at the University of Texas at Austin and the University of California-Los Angeles reveal that "men are more likely to regret not seizing the moment for a quick and meaningless tryst, while women are more remorseful about actually jumping into bed for a one-night stand," writes Meg Sullivan at the UCLA Newsroom.

The findings, published in the most recent issue of Archives of Sexual Behavior, include data from three different studies, one of which included over 24,000 participants. Overall, the research found that men and women engage in casual sex in equal amounts, and men's and women's regrets (or lack thereof) over casual sex are similar regardless of sexual orientation.

But the robust correlations between having a vagina and regretting sexual encounters, and having a penis and not having more of said sexual encounters led the researchers to believe evolution may be at the root of this divide. Martie Halston, a UCLA professor on the study, says:

For men, throughout evolutionary history, every missed opportunity to have sex with a new partner is potentially a missed reproductive opportunity — a costly loss from an evolutionary perspective. But for women, reproduction required much more investment in each offspring. The consequences for casual sex were so much higher for women than for men, and this is likely to have shaped emotional reactions to sexual liaisons even today. [UCLA Newsroom]

I disagree: It's hard to see how this data supports an evolutionary understanding of sexual behavior.

For one, I always find it hard to believe that modern young men's sexual decisions are guided by an evolutionary desire to reproduce with as many women as possible, when most are terrified by the thought of accidentally getting someone pregnant.

Here's a thought: Maybe the reason men desire to sleep with more people is that they are much more likely to orgasm from casual sex than women. Granted, their ability to more easily orgasm can be seen as a product of evolution, but the female orgasm has also been shown to be an important factor in increasing the likelihood that sperm is retained (and a baby is made). If men were fueled by that evolutionary desire to procreate, you'd think they would care a lot more about the women in their casual sexual encounters having an orgasm. But they don't.

In fact, an examination of the top sexual regrets for women reveal that social pressure may play as much, if not more, of a role than evolution.

Remember, the most common regret for women was losing their virginity to the wrong person. The second most common was cheating on a past or present partner. Let's look at both:

1. When it comes to virginity, women face daunting social pressure. In America, virginity is fetishized, and a woman's decision to have sex for the first time is often depicted as a life-changing, monumental decision. While in theory, this too, could be argued as a result of evolution, the fact that some cultures take virginity pressure to an extreme (like the ones where hymenoplasty is becoming popular) while others are finally starting to treat virginity as not that big of a deal (thank you, Aubrey Plaza) suggests it's not as much a biological as a social convention.

2. The regret around cheating may suggest that women value fidelity more than men (since cheating didn't crack the top list for men). That could be an evolutionary result. Or it could be that women have faced greater pressure to avoid the historical stereotype of spinsterhood, and, therefore, have learned to prioritize maintaining the stability of a long-term monogamous relationship. No wonder they feel worse when they cheat, then.

It's hard to tease out what is purely evolutionary and what is a result of cultural and social factors when it comes to human behavior, especially one as complex and highly depicted in mainstream entertainment as sex. Women may feel regret over the sex they had because it could have endangered them thousands of years ago, or because society has imbued them with fears of being labeled a slut. And men may feel regret over not having more sex because their ancestors needed to sleep with as many women as possible to have a good shot at advancing their genes, or because there are a ton of movies that say they are wusses for not having lots of sex.

Unfortunately, the only thing that seems clear is that as long as people have sex, they'll be having regrets, too.